The mother of one of the girls charged with brutally stabbing a 12-year-old friend to appease the fictional “Slender Man” character says her daughter is mentally ill and should not be charged as an adult.

“I was shocked to learn 12-year-olds can be charged as adults,” said Angie Geyser, 36, the mom of Morgan, now 14. Morgan and Anissa Weier were 12 when both were charged with luring classmate Payton Leutner into a wooded area and stabbing her 19 times, authorities said.

Morgan’s mother spoke publicly for the first time about her daughter when she spoke with the Milwaukee Journal-Sentinel last week.

“You can’t hold somebody responsible for the rest of their life for something they did when they were 12,” Angie Geyser told the paper.

Morgan has been diagnosed with early onset schizophrenia since she’s been in custody, her mother said. Her father also suffers from the same mental illness, but Geyser said the disease doesn’t usually manifest itself until early adulthood.

Both girls have pleaded not guilty and the Geysers say the cases should be moved to juvenile court. Each is being held in lieu of $500,000 bail.

“Some of the comments on stories say ‘Adult crime, adult crime.’ That’s BS. These are children,” the mother said.